"Killer" in our midst - Kick 'em Jenny

by Terry Ally
WEEKEND NATION
Aug 29, 1997

It's virtually a snowball's chance in Hell of there being such a cataclysmic eruption from the submarine volcano Kick 'em Jenny to generate a large enough wave to destroy Barbados' west and south coasts.

Not that it was impossible, said experts, but it was highly unlikely.

What they do say is that as the volcano gets closer to the surface an eruption would trigger a tsunami (giant wave). A big eruption would send giant waves hurling through the Caribbean Sea, at the speed of a commercial jetliner, hitting virtually every country from Venezuela to St. Maarten. A smaller eruption would not generate very large waves.

The volcanology group at the University of Lancaster created "worst case" and "realistic" computer simulations showing the time the waves would reach the islands and height.

At worst, Barbados would be hit with a 3 to 4 metre high tsunami while Grenada would be hit by waves 46.11 metres, and Carriacou 28.39 metres. In the northern Caribbean, St. Maarten would see 28 to 29 metre-high tsunamis.

The "realistic" scenario was between 0.5 to 1 metres for Barbados, 7 to 8 metres for Grenada and 5 metres for Carriacou. In addition, ships could be severely damaged by the blast.

Damage to each island, under each scenario, was anyone's guess because no risk assessment studies were ever done. Barbadians would not know when a tsunami was coming, how soon it would arrive, how far inland it would travel, the power it would punch to wash away people from the beaches, cars or houses along the coast or the amount of damage it could cause to buildings, roads or utilities.

The seriousness of the situation is that the volcano is rising to a critical height at which a blast could be powerful to trigger tsunamis. Experts however believe that though the worst-case scenario was not impossible, it was not highly probable.

"We do not expect it to be as violent as a Krakatau but as volcanologists, we do not rule out such," said Lloyd Lynch, research fellow of the Seismic Research Unit of the University of the West Indies.

"I personally think that is unlikely," said Dr. Haraldur Sigurdsson, Professor of Oceanography at the University of Rhode Island, one of the foremost experts on Kick 'em Jenny. I think tsunamis of the order of 1 to 2 metres would possibly affect Barbados but were unlikely to be any larger than that," he said.

"It seems that an event on the scale of Krakatau is unlikely . . . before the volcano breaches the sea surface, but it cannot be ruled out," stated Dr. Martin Smith and Dr. John Shepherd of the Environmental Science Division, Lancaster University, in a published paper.

The 1883 underwater blast from Krakatau in Indonesia, was heard over one-thirteenth of the earth's surface. Rocks were thrown 34 miles high and ash fell 3 313 miles away. The giant wave it triggered wiped out 163 villages with 38 380 people in them up to 800 km away, yet Krakatau was only about one-fifth of the Santorini explosion in Greece, c1550 BC, which destroyed the island and possibly gave rise to the myth of Atlantis.

Located nine kilometres north of Grenada, between Grenada and Carriacou and immediately east of Ronde Island, the submarine volcano sprung into the news when Christian prophets in Barbados predicted, two weeks ago, that it would erupt this year and trigger tsunamis which would impact severely in the island's west and south coasts.

Highly active volcanoes generally tend to give a big bang and then drift off to sleep 

until it erupts hundreds of years or a few decades later. Kick 'em Jenny is not one of those. With eleven eruptions in 52 years it is the most active volcano in the Caribbean erupting, at least, once every decade.

Shepherd, another leading expert on Kick 'em Jenny, has been studying the links between submarine volcanic activity and tsunamis. The computer simulations created by his volcanology group were based on the Volcano Explosivity Index or VEI. VEI is for volcanoes what the Richter Scale is for earthquakes.

The "realistic" scenario was based on a VEI-3 which represents an explosion 10 times more powerful than the 1939 explosion of Kick 'em Jenny which produced tsunamis between one to two metres that damaged St. George's Habour. The worst-case was a VEI-6 which was the Krakatau explosion.

Coastal damage

No one knows for sure what would happen if a tsunami of any size hit a Caribbean island. There were no studies on it though such information was needed to alert the public and put rescue measures in place.

"We don't really know the extent of the communities at risk, we need to do some studies of the vulnerabilities aspect, the number of coastlines which could be affected, given scenarios," said Lynch. As a mere guess, Lynch said that a 5 to 10 metre tsunami could travel 200 to 300 metres inland of the St. George's Harbour, Grenada.

The top of the cone of the volcano, which was 262 metres below the surface in 1972, was measured at 150 metres in 1989 by Sigurdsson. It was now approach "shallow water" - that "danger zone" of less than 100 metres where the water pressure is reduced.

"We think that when the crater becomes very shallow, the explosions will be larger and there will be more ash fall," said Sigurdsson.

That ash fall will be primarily on Carriacou and Grenada. However, in the event of a large eruption when the ash reaches the upper atmosphere, the winds will take it west to east, towards Barbados.

"If the eruptions are quite large . . . Kick 'em Jenny ash will be falling on Barbados in the future, just as the eruptions of St. Vincent Soufriere produced ashfall on Barbados in 1979," said the professor.

At the same time, any ships passing over the volcano at the time of explosion would be blown out of the water.

 

Kick 'em Jenny
at a glance

  • It's located between Grenada and Carriacou and immediately east of Ronde Island. It about about 9 km off the north coast of Grenada.
  • It is the most active volcano in the Caribbean and one of 105 underwater volcanoes in the world.
  • It erupts, on average, every 4 to 5 years.
  • There were eruptions in 1990, 1989, 1988, 1977, 1974, 1972, 1966, 1965, 1953, 1943 and 1939, but others could have occurred.
  • At 1200 metres high, it is the tallest mountain in the region.
  • In 1972, Professor Haraldur Sigurdsson of the University of Rhode Island measured the top of the cone at 262 metres beneath the surface. During his last dive, in 1989, it was 150 metres from the surface, making it one of the fastest growing mountains.
  • When the cone is less than 100 metres below sea level, explosions will be more powerful and penetrate into the atmosphere because there is less water pressure.
  • A large eruption will cause ashfalls on Barbados, and tsunamis on Grenada and Barbados.
  • Depending on the size of the eruption, tsunamis could reach as far as St. Maarten and Puerto Rico.
  • A cataclysmic eruption, triggering devastating tsunamis on Barbados, was highly unlikely.
  • In the next 20 years, it will give birth to the newest island in the Caribbean.
Other Kick em Jenny stories

See also:

Recommended reading:

Seismic Research Unit - Trinidad
Background on Kick 'em Jenny
Other West Indies volcanoes - Mont Pelée, Soufriere Hill
UVI scientists study underwater volcano "Kick 'Em Jenny" -- Link courtesy University of the Virgin Islands
Smithsonian's Global Volcanism Program - Kick 'Em Jenny
Plate Tectonics and Seafloor Spreading
Near-Real time global seismic records